1. The Field
A composition is disclosed in which a dry powder or liquid blowing agent is mixed into either a base blend or a liquid mixture. The base blend is formed of one or more dry mineral fillers such as mechanically processed fly ash. Thereafter, the other ingredients are added to the base blend and compounded to form a masterbatch or to form a fully compounded material both of which are processed at a temperature at which the blowing agent is not activated. More specifically, an acid scavenger, an antioxidant, a suitable carrier resin, a particle compatibilizer and an impact modifier may be mixed with the dry filler blend to form a masterbatch that is thereafter combined with a base resin (which may be the same as the carrier resin) and an additional low or fractional melt resin to form the fully compounded material. Alternately, all the ingredients may be combined at once to form the fully compounded material. Also, alternately, the composition may be formed as a mixture without the blowing agent; and the dry powder blowing agent is thereafter mixed in as that mixture is heated into liquid form just before mechanical processing into a product. The final product after mechanical processing is less dense while having an impact resistance equal to or greater than the impact resistance of a similar product formed from a base resin having a blowing agent mixed therein.
2. The Relevant Technology
A plastic like polyethylene and/or polypropylene is typically selected for desired physical properties, some of which can be controlled using additives that include, among others, colorants, lubricants, stabilizers, foaming agents and various fillers. Traditionally, fillers have been used to lower the cost of a composition and in turn the resulting product because expensive resin is being replaced by less expensive filler. Specific fillers called reinforcing fillers are also known to be used to alter some of the physical properties of the base resin, such as tensile and flexural strength, hardness, impact resistance, shear and other rheological and morphological characteristics of the resulting compounded material. Blowing agents have also been used to reduce the amount of resin used but also to control physical properties such as the density of the finished product.
It is known that one may add a blowing agent in the process of manufacturing a product while the compounded material is in liquid form. When the blowing agent is activated in the manufacturing process, the blowing agent produces a gas which in turn makes the liquid resin and resulting solid material less dense. In other words, less resin is used to form essentially the same product thereby reducing the amount of compound and in turn base resin used to form a particular product due to the formation of gas filled bubbles or pockets within the product.
Fillers and blowing agents are also known to have some effect on processing characteristics of thermoplastic resins while molten. For example, unfilled polymers behave like non-Newtonian fluids with viscosity changing during melt processing. Some additives affect the rheology except that increasing the amount of the filler (regardless of the shape of the particles of the filler) has been reported to lead to reduced melt elasticity. M. Xanthos, Functional Fillers For Plastics (Wiley-VCH 2005) pp. 32-35.
Fly ash, cinders and combinations of fly ash and cinders have been identified as fillers that can be used with resins in a beneficial manner as disclosed in U.S. Pat. No. 7,879,939 (Prince et al.) (hereinafter the '939 patent).
Fly ash is a waste material that is comprised of various minerals which are the residue formed during the combustion of hydrocarbons like coal, typically in large volume processes like those associated with the generation of electrical power. As the coal is burned, a residue or “ash” is formed that is so light that it can be regarded as buoyant in air. The fly ash may include cinders formed during coal combustion. The cinders are typically made from fused or other non combustible matter that was part of the coal. Large cinders typically fall to the bottom in the combustion zone or area. Some smaller or lighter cinders can become entrained in the exhaust stream along with fly ash.
Fly ash, as well as the cinders, can vary in chemical and physical properties based on, among other things, the specific source of the hydrocarbon being combusted and the particulars of the combustion process. In turn, fly ash, by itself and also together with cinders, has not been used as a filler for thermoplastic compositions on a commercial scale because physical and chemical properties are not consistent.
To create a standard or consistent fly ash composition that is suitable for use on a commercial scale with thermoplastic resins, U.S. Patent Application Publication No. 2011/0071252 published Mar. 24, 2011 (the '252 Publication) for a “SYSTEM AND METHOD FOR FORMING A COMPOSITION WITH AN OPTIMIZED FILLER” discloses methods and procedures to select or form an optimized filler or blend of fillers. In other words, fly ash, with and without cinders, can be mechanically treated and blended or otherwise mixed to form a filler or blend of fillers that is useful in forming thermoplastic compositions as disclosed in the '939 patent.
It is known to use certain fillers with thermoplastic resins to alter the toughness or impact resistance properties for the manufacture of a wide variety of products. But it has not been known how to formulate such products that are both tough and less costly to manufacture and how to formulate to vary the physical properties such as the toughness while reducing cost and reducing density by use of blowing agents.